Impulse direction-finding method



Aug. 12, 1941. G. ULBRICHT IMPULSE DIRECTION-FINDING METHOD 5/200 TUBEFiled Feb. 11, 1938 mrpaLst F050.

sweep osc IVG - IMPULSE rem. swap osc.

r m U r e h t n u G Gttorneg Patented Aug. 12, 1941 IMPULSEDIRECTION-FINDING METHOD Gunther Ulbricht, Blankenfclde Mahlow, Germany,assignor to Telefunken Gesellschaft fiir Drah-tlose Telegraphic m. b.H., Berlin, Germany, a corporation of Germany Application February 11,1938, Serial No. 190,105 In Germany February 3, 1937 of this tubeappears across the plate load im- 4 Claims.

This invention relates to impulse direction finders and has for itsobject the provision of an apparatus for and a method of increasing theeffective separation between two successive impulses, such as the groundand space wave impulses in a directionfinder.

This invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing, in whichFigure 1 illustrates the result of the overlapping of two successiveimpulses,

Figure 2 illustrates an embodiment of my invention which utilizescapacitive coupling between the radio frequency rectifier and the audiofrequency rectifier,

Figures 3a and 3b represent, respectively, an impulse as received andthe impulse which is derived therefrom. Fig. 3c is a special case of theimpulse shown in Fig. 3b,

Figures 4a and 4b represent, respectively, received and derived groundand space waveimpulses of substantial spacing and received.and derivedground and space wave impulses of small spacing such as is shown in Fig.l',

Figure 5 is a schematic drawing of an alternative embodiment of myinvention which utilizes transformer coupling.

The working ranges obtainable with the impulse direction-finding methodsare limited for the reason that when the major or original signals andthe echo or space signals are received at a great distance from thetransmitter it is no longer possible to separate the two as they occurin such rapid succession. In fact, they merge into one another andoverlap partly as shown in Fig. 1 where the amplitudes of the mainsignal H and of the echo E are plotted against the time t.

According to the invention an increase in the working range or distancecan be attained by reducing the time duration or width of the incomingspace and ground wave impulses at the receiver, with a view toseparating them. more clearly as to their time of arrival. To accomplishthis the radio frequency impulses are rectified and the resultantunipotential impulse signals are coupled through energy storing means toan audio-frequency rectifier.

Referring to Fig. 2, one embodiment of my invention is shown whichutilizes a resistancecapacitance coupling system. A loop antenna L isused to receive the impulse signals. The signal is then impressed on thegrid of a radio frequency rectifier tube HG. The rectified outputpedance n, and a voltage is impressed on the grid of the audio frequencyrectifier NG by the coupling capacitor C. The rectified voltage whichappears across the output impedance T2 'is impressed across the verticaldeflecting plates of a Braun tube B. The horizontal deflecting plates ofthe Braun tube are connected to a sweep oscillator which is synchronizedto the frequency at which the impulses occur. This provides a horizontalscanning line on which a mark appears whenever an impulse is received.Impulses arriving at difierent times appear in different positions onthe line and may thus be identified. The use of a loop antenna and aBraun tube indicator for impulse direction finding are in themselvesold.

The operation of my invention will now be explained.

'Afteri radio frequency rectification in rectifier HG the voltage acrossthe resistance '11 corresponding to one impulse has the form shown inFig. 3a. The voltage appearing across the resistance R is the derivedcurve as shown in Fig.

. 3b. This will be understood when it is remem-' bered that the voltagewhich is induced through a capacitor, or a transformer, i zero when theinducing voltage is constant, and a maximum when the rate of change ofthe inducing voltage Mathematically, the

relation between the inducing and the induced voltage is expressed bythe process of diiferentiation. Thus a sine wave voltage, or current,induces a'voltage which follows a cosine curve. An impulse such as thatshown in Fig. 3a is not the equivalent of one half of a sine wave cycle,for in the sine wave the rate of change is a maximum at the point ofintersection with the abscissae while in the impulse the rate of changebecomes zero at the point of intersection with the abscissae.

The width of the impulse is decreased because the derived voltage startsfrom zero, goes through a maximum and returns to zero in the time duringwhich the original voltage is going from zero to maximum. The return ofthe original voltage to zero induces another impulse of oppositepolarity. The two derived impulses are shown at FI and F2 of Fig. 3b.The areas Fl and F2 above and below the neutral or zero line must be thesame since no direct current will flow through the condenser C. The formof the areas is a function of the size of condenser C and of theresistance R.

In the impulse direction-finding method the signals follow one anotherperiodically, say, at a frequency of f1=300 cycles per second. If thecoupling means C and R are chosen so small that only the high harmonicsof frequency h are transmitted, then the signals which appear across Rassume the shape shown in Fig. 30.

Now, these signals are fed to the grid of the audio frequency rectifierNG. Owing to rectification, the negative portion below the neutral linedrops out, and there is obtained in the output of the tube across theresistance r2 signals of the original shape, though narrowed orconstricted. In this manner both the ground wave impulse and the echosignal will be reduced in width. If the ground wave and the echoimpulses are received with as great a separation as that illustrated inFig. 4d at a, their identification would be possible according to theusual methods, but by utilizing the method herein explained theirseparation would be improved as shownin Fig. 4a at a. However, if theground wave and the echo impulses are received in very close sequence asshown at b in Fig. 4b, or in Fig. 1, then, as noted above, directionfinding would normally be quite inaccurate. By my invention, the twoimpulses are completely separated as shown at b in Fig. 4b,

and direction finding thusmade" accurate where" it is otherwiseinaccurate.

In Figs. 4a and 4b the vertical dotted lines are drawn in to show therelative time relationbe tween the received impulses'at a'and' b and thederived impulses at a" and b; The dotted lines below the abscissae showthat portion of the derived voltage which has been removed by the audiorectifier NG.

Referring now to Fig. 5, an alternative arrangement is illustrated whichsubstitutes. a transformer coupled stage for the impedance-capacitancecoupling shown in Fig. 2. The theory'of operation is the same as before,as it is well known that the voltage induced in the secondary 'ofa' 2.The combination which includes means re-' ceptive to short radiofrequency ground wave impulses, said means being receptive to undesiredreflected impulses which arrive at a normally indistinguishableintervals after said ground wave impulses, means for rectifying saidground wave and said reflected impulses, a capacitor coupled to saidrectifying means for obtaining an impulse transformer is the derivativeof the primarycur rent.

ing the received impulses, obtaining a derived The basic idea of thisinvention is. not confined to its use as here suggested and the energystorl which is the derivative of each of said rectified impulses, thetime duration of said derivative impulse being small with respect to theduration of each of said received impulses, means for rectifying saidderived impulses, and means for indicating the successive occurrence ofsaid derived and rectified impulses to distinguish said ground waveimpulse from said reflected impulse.

3. The combination which includes means receptive in short radiofrequency ground wave impulses, said means being receptive to undesiredreflected impulses which arrive at a normally indistinguishable intervalafter said ground wave impulses; means for rectifying said ground waveand said reflected impulses, a transformer coupled to said rectifyingmeans for obtaining impulseswhich are the derivatives of said rectifiedimpulses, the time duration of said derivative impulses being small withrespect to the duration of corresponding received impulses, means forrectifying said derived impulses, and means for indicating thesuccessive occurrence of said derived and rectified impulses todistinguish said grx'gund wave impulses from said reflected imp se.

'4. The combination which includes means receptive to short radiofrequency impulses, means for rectifying said impulses to obtainunipotential impulses containing high order harmonics, means forobtaining derivative impulses from said high order harmonics of saidrectified impulses, means for rectifying said derivative impulses, andmeans for visually indicating the successive occurrence of saidrectified derived impulses.

GUNTHEB, U'LBRICH'I.

